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F-region ionospheric structure associated with antisunward flow near the dayside polar cusp


  • John D. Kelly,

  • James F. Vickrey


After one year of measurements using the Sondrestrom incoherent-scatter radar (74° Λ), a number of repeatable features have been identified that interrelate the F-region ionization and plasma convection patterns. One of these is an extended (poleward) ridge of ionization frequently present overhead near magnetic local noon. This ionization enhancement is associated with large ion drift velocities with a significant poleward component. Similar ionization features have been reported and thought to be produced by convection of F layer plasma through an ionization source—soft particle precipitation associated with the polar cusp. In this study, however, we are able to measure the electron temperature as well as number density and drift velocity. These measurements indicate that the electron temperature is not elevated within the density enhancement suggesting that the enhancement is not caused by local soft particle precipitation. Rather, it may simply be F-region plasma convected from lower latitudes with correspondingly lower solar zenith angles.

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